The Agricultural Health Study (AHS) is a prospective cohort study of 89,655 licensed private pesticide applicators (mostly farmers) and their spouses from North Carolina and Iowa, and licensed commercial pesticide applicators from Iowa. Since enrollment in 1993 to 1997, AHS participants have been followed through various methods to study cancer and chronic disease outcomes. Surveys in 1999 to 2003, 2005 to 2010, and 2013 to 2015 have collected information on a range of self-reported chronic disease diagnoses, symptoms, and covariates. Over half the cohort is over age 65 years of age, and increased aging-related morbidity and mortality may impact future cohort participation and bias research findings, if diseases are related to pesticides as well as loss to follow-up. Recent response rates were as low as 61% and over 16% of the cohort is deceased, while only 8% of participation in the recent survey was by proxy (mostly for deceased participants). Many diseases require additional confirmation and validation of self-reported diagnoses, and response rates to these efforts are similarly limited. This project links data on 48,118 Medicare-eligible AHS participants with administrative health records, including diagnostic codes and other data, to supplement information already collected in the AHS and to identify chronic diseases that have not been identified by AHS questionnaires.